As one skilled in the field of aeronautical technology appreciates, it is conventional to provide dampers, particularly for the blades in a turbine rotor of a turbo-pump for rocket engines or the turbine blades of a jet engine, that serve to attenuate the high vibration occasioned by the hostile environment to which this hardware is subjected. Typically, one of the more conventional methods of damping is to have the damper made to provide damping from blade to blade. However, the problem with a blade-to-blade damper is that the damping can only be tuned to just a few specific modes of vibratory motion and does not attenuate vibratory motion in other modes. In the blade-to-blade dampers the frictional resistance is created between blades whereas the type of damper that is the subject matter of this invention the frictional resistance is created between the blade and ground as will be detailed in the description to follow. Other dampers utilized in the aeronautical field are dampers that serve to create the frictional resistance between blades and the disc supporting the blades, which is essentially a blade to ground damper. In these types of dampers the damping occurs between blade and hardware that is grounded in the system. Typically this method of damping is primarily concerned with vibrations occurring in the axial and circumferential direction.
Examples of blade-to-blade damping is described in U.S. Pat. No. 4,872,810 granted to Brown et al on Oct. 10, 1989 entitled "Turbine Rotor Retention System" and commonly assigned to United Technologies corporation. An example of damping that is created between the blade and disc or blade to ground damping is in U.S. Pat. No. 5,205,713 granted to Szpunar et al on Apr. 27, 1993 entitled "Fan Blade Damper" which discloses a damper where the damper is reacted against the platform of the blade and transmitted to the turbine disk where the damper is mounted in a statically determinant fashion. In another type of damper the center of gravity is offset from the point of contact and this type of damper is exemplified by U.S. Pat. No. 5,052,890 granted to Roberts on Oct. 1, 1991 and entitled Device For Damping Vibrations in Turbo machinery Blades. All of these aforementioned patents are of the type that react the vibratory motion from blade-to-blade or blade-to-disc notwithstanding that the damper acts on the platform of the blade and the reaction may be in the disc and in all of these systems the damping occurs in a circumferential and/or axial direction.
The problem that needed to be solved by this invention is where the vibratory motions that are encountered in the turbo-pump of a rocket engine or the turbine of a gas turbine engine pumps, etc. where there are many sources of cyclic or periodic loads on individual components of the system and the loads needed to be damped are in the radial direction. The rotating turbine blades are subject to vibratory excitations caused by these oscillating loads. These vibratory excitations induce a dynamic stress in addition to the steady stress in the blade which can cause fatigue cracking and eventual catastrophic failure of a blade. The dampers serve to generate friction during the motion of the blade and damper which generates heat and dissipates the energy created by the vibratory motion with a consequential reduction in lower cyclic stress. In other words and in accordance with this invention the damping lessens the amplitude of motions in the radial direction during the vibratory excitation so the designers of rotating machinery utilize this damping technique to avoid high cycle fatigue.
It is customary to provide a mass or small piece of hardware against two adjacent blades or blade and disc and rely on the centrifugal force of the rotating machinery to press the hardware against the working surface of the blade/blade or blade/disc. As one skilled in this art knows, this type of blade/blade or blade/disc damper is satisfactory where it is desired to attenuate the vibrations in a circumferential direction and/or axial direction. Unfortunately, these types of dampers referred to in the immediate above paragraphs do not damp in the radial direction and hence, the vibratory motion incidental to radial loads are not attenuated.
In experimental testing of the fuel pump used in rocket engines, it was found that cracking and eventual failure of turbine blades had been experienced when utilizing the heretofore known types of dampers, i.e. the blade-to-blade dampers.
We have found that we can obviate this problem by providing a damper that resists the radial motion and achieves a blade-to-ground damping rather than the blade-to-blade damping. The damper which is a small mass or metallic hardware that is geometrically and judiciously configured to fit into a radial recess or slot formed in the surrounding hardware and the center of gravity of the damper is offset relative to the point of contact that the damper makes with the adjacent part, be it the blade or blade platform. The slot is formed in either in the disc or blade. During high rotational velocity of the rotating machinery the damper of the present invention is forced radially outwardly to press against the turbine blade. The reaction forces induced against the side wall in the slot serve to attenuate the vibration occurring in the radial direction. It will be noted that although these dampers of this invention are efficacious for damping vibratory motion in the radial direction, the use of other dampers for treating vibratory motions in other directions are not precluded.